The present invention relates to an hydraulic control system which controls the flow of fluid to at least two consumers. Associated with each consumer is a pressure-compensated direction-reversing valve. Each valve performs a throttling function and a pressure-compensation function to establish a selected volumetric flow rate, and also a direction-control function.
German published patent application DT-OS 24 40 099 discloses a control system of this general type in which, in order to avoid energy losses, the output power of the pump of the control system is automatically adjusted to meet the prevailing demand of the system. In that system, the control spools of all direction-reversing valves are arranged one after the other between the pump (which is of adjustable per-cycle volumetric throughput) and the tank, and provided between the last control spool and the tank is an adjustable constrictor, the pressure drop across which is used to control an auxiliary control valve, which in turn effects adjustment of the per-cycle volumetric throughput of the pump. This purely hydraulic system has the disadvantage that the expense for the hydraulic lines is relatively high. Also, the system tends to be inexact and somewhat insensitive in operation. Above all, the system does not operate reliably during reversals of flow direction.